Department of Botany, University of Toronto, Toronto, Ontario, M5S 1A1, Canada.
Plant Physiol. 1977 Dec;60(6):862-7. doi: 10.1104/pp.60.6.862.
An absolute requirement for divalent cations is reported for H(14)CO(3) (-) influx in Chara corallina. Effective substitution of eluted Ca(2+) by Mg(2+) and Sr(2+) was observed, but Mn(2+) was completely ineffective in restoring H(14)CO(3) (-) transport activity. Similarly, La(3+) could not substitute for Ca(2+) in this system. Low concentrations of ethylenediaminetetraacetate (0.01 to 0.06 mm) significantly enhanced the rate at which H(14)CO(3) (-) transport capacity was lost.Examination of the response of OH(-) efflux, during Ca(2+)-free treatment, indicated that the cellular control over OH(-) efflux remained unaffected until membrane integrity became severely affected. This conclusion was supported by the response of OH(-) efflux to 10 mm K(+). Therefore, assimilation of H(14)CO(3) (-) is not rate-limited by an effect of Ca(2+) elution on the OH(-) transport system. Kinetic experiments indicated that Ca(2+) removal from the membrane resulted in noncompetitive inhibition of H(14)CO(3) (-) assimilation; the apparent Michaelis constant remained unaltered over a wide range of conditions. An hypothesis is presented which suggests that membrane integrity is necessary for HCO(3) (-) transport to occur, but Ca(2+) (Mg(2+), Sr(2+)), per se, must be bound to the transport complex before activity is established.
报道称，二价阳离子是小球藻中 H(14)CO(3) (-)内流的绝对要求。观察到洗脱的 Ca(2+)被 Mg(2+)和 Sr(2+)有效取代，但 Mn(2+)完全不能恢复 H(14)CO(3) (-)转运活性。同样，La(3+)不能在该系统中替代 Ca(2+)。低浓度乙二胺四乙酸（0.01 至 0.06mm）显著提高了 H(14)CO(3) (-)转运能力丧失的速度。在无 Ca(2+)处理期间考察 OH(-)外排的反应表明，细胞对 OH(-)外排的控制在膜完整性受到严重影响之前仍然不受影响。这一结论得到了 10mm K(+)对 OH(-)外排反应的支持。因此，H(14)CO(3) (-)的同化不受 Ca(2+)洗脱对 OH(-)转运系统的影响所限制。动力学实验表明，从膜中去除 Ca(2+)导致 H(14)CO(3) (-)同化的非竞争性抑制；在广泛的条件范围内，表观米氏常数保持不变。提出了一个假设，即膜完整性是 HCO(3) (-)转运发生所必需的，但 Ca(2+)（Mg(2+)，Sr(2+)）本身必须与转运复合物结合才能建立活性。
